Deciphering the Molecular Basis of Cadmium Stress Adaptation in Lentinula edodes: Genome-Wide Identification of MAPK Cascade Genes and Their Functional Characterization

Mitogen-activated protein kinase (MAPK) cascades play a central role in eukaryotic signal transduction, regulating diverse biological processes including development and stress responses. However, despite Lentinula edodes being the most widely cultivated edible mushroom worldwide, its MAPK cascade gene families remain uncharacterized, and their involvement in cadmium (Cd) stress responses is completely unknown. In this study, we performed genome-wide identification of MAPK cascade genes in L. edodes, uncovering 16 members comprising three LeMAPKKK genes, four LeMAPKK genes, and nine LeMAPK genes. Phylogenetic and homology analyses classified these genes into three putative MAPK cascade pathways. qRT-PCR analysis demonstrated strain-specific, concentration-dependent, and temporally dynamic expression patterns under Cd stress. Notably, four genes (LeMAPK1, LeMAPK7, LeMAPKK2, and LeMAPKKK1) exhibited consistent upregulation across both strains and high Cd concentrations (1 and 10 mg/L) at the 7 h time point. Based on these findings, we propose a working model for Cd stress response in L. edodes centered on these core regulatory genes. These findings may inform breeding strategies for low-Cd-accumulating cultivars and the optimization of cultivation practices to reduce Cd content, with potential implications for the sustainable development of the L. edodes industry and human health.